Sulfur-containing imidazole fiber having ionically bonded halides

ABSTRACT

The present invention concerns fiber made from a polymer comprising imidazole groups, fiber further having: i) a halide anion, the halide anion being present in an amount of 0.05 to 20.1 weight percent, based on weight of fiber; and ii) sulfur, wherein the sulfur is present in the fiber in an amount of 0.05 to 3 weight percent; the fiber exhibiting hydrochloric acid evolution as identified by TGA-IR between 277.13° C. to 448.19° C.

TECHNICAL FIELD

The present application concerns sulfur-containing imidazole fiberhaving ionically bonded halides.

BACKGROUND

Advances in polymer chemistry and technology over the last few decadeshave enabled the development of high-performance polymeric fibers. Forexample, liquid-crystalline polymer solutions of rigid-rod polymers canbe formed into high strength fibers by spinning liquid-crystallinepolymer solutions into dope filaments, removing solvent from the dopefilaments, washing and drying the fibers; and if desired, further heattreating the dried fibers to increase tensile properties. One example ofhigh-performance polymeric fibers is para-aramid fiber such aspoly(paraphenylene terephthalamide) (“PPD-T” or “PPTA”).

Fibers derived from 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI),para-phenylenediamine (PPD) and terephthaloyl dichloride (TCl) are knownin the art. Hydrochloric acid is produced as a by-product of thepolymerization reaction. The majority of the fibers made from suchcopolymers have generally been spun directly from the polymerizationsolution without further treatment. Such copolymers are the basis forhigh strength fibers manufactured in Russia, for example, under thetrade names Armos® and Rusar®. See, Russian Patent Application No.2,045,586. However, the copolymer can be isolated from thepolymerization solvent and then redissolved in another solvent,typically sulfuric acid, to spin fibers, as provided for example, inSugak et al., Fibre Chemistry Vol 31, No 1, 1999; U.S. Pat. No.4,018,735; and WO 2008/061668.

Known processes for making copolymer fibers directly from polymerizationsolution, while producing a good product for use in ballistic and otheraramid end-uses, are very expensive with very poor investment economics.As such, there is a need in the art for manufacturing processes whereinthe copolymer is solutioned in a common solvent, such as sulfuric acidwhich has improved economics compared to processes known in the art.

Previously, it has been assumed that fibers derived from copolymers of5(6)-amino-2-(p-aminophenyl)benzimidazole, para-phenylenediamine andterephthaloyl dichloride and solutioned from sulfuric acid could be spuninto to high quality fibers using processing similar to that used formaking PPD-T fibers, since the compositions appear similar. However, ithas been found that spinning the copolymer into high tenacity fibers hasunique challenges that are not present in the PPD-T framework and newtechniques are needed. Since higher tenacity fibers can provide moreutility due to their strength per unit weight, improvement in tenacityis welcomed.

SUMMARY

The present invention concerns fiber made from a polymer comprisingimidazole groups, fiber further having: i) a halide anion, the halideanion being present in an amount of 0.05 to 20.1 weight percent, basedon weight of fiber; and ii) sulfur, wherein the sulfur is present in thefiber in an amount of 0.05 to 3 weight percent, based on weight of thefiber. In some embodiments, the halide anions are present in an amountof 0.1 to 5 weight percent. In certain embodiments, the halide anionsare present in an amount of 0.1 to 1 weight percent.

In certain embodiments, the polymer comprises residues of5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine, andaromatic diacid-chloride. In certain embodiments, the aromaticdiacid-chloride is terephthaloyl dichloride. In certain embodiments, thearomatic diamine is para-phenylenediamine. For some preferred polymers,a stoichiometric amount of terephthaloyl dichloride relative to the sumof the amount of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromaticdiamine is utilized in forming the polymer. In some embodiments, themolar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromaticdiamine is in the range of from 30/70 to 85/15. In certain embodiments,the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromaticdiamine is in the range of from 45/55 to 85/15.

Some fibers contain halide anions which comprise one or more of F—, Cl—,Br—, and I—. Certain fibers contain one or more of Cl— and Br— anions.

Some fibers of the invention have a sulfur content of 0.01 to 2.5 or 0.1to 1.75, or 0.1 to 1.0 or 0.01 to 0.08 or 0.01 to 0.05 weight percentbased on the weight of the fiber.

In some aspects, the invention concerns yarns comprising fibers of theinvention. Some yarns have a tenacity of 32 cN/dtex (35.6 gpd) or higheror 34 cN/dtex (37.8 gpd) or higher or 36 cN/dtex (40 gpd) or higher.

Yet another aspect of the invention concerns fabric comprising the yarnof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, isfurther understood when read in conjunction with the appended drawings.For the purpose of illustrating the invention, there is shown in thedrawings exemplary embodiments of the invention; however, the inventionis not limited to the specific methods, compositions, and devicesdisclosed. In the drawings:

FIG. 1 is a schematic diagram of a fiber production process.

FIG. 2 presents TGA-IR identification of HCl evolution results for: A.Aramid copolymer sample that contains chloride anions with nochlorinated monomer. B. Aramid copolymer sample that containschlorinated monomer with no chloride anions.

FIG. 3 presents TGA-IR weight loss results from aramid copolymer samplethat contains chloride anions with no chlorinated monomer.

FIG. 4 presents TGA-IR weight loss results from aramid copolymer samplethat contains chlorinated monomer with no chloride anions.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description taken in connection with the accompanyingfigures and examples, which form a part of this disclosure. It is to beunderstood that this invention is not limited to the specific devices,methods, conditions or parameters described and/or shown herein, andthat the terminology used herein is for the purpose of describingparticular embodiments by way of example only and is not intended to belimiting of the claimed invention.

In some embodiments, the polymer comprises residues of5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine, andaromatic diacid[chloride]. Suitable aromatic diacid chlorides includeterephthaloyl chloride, 4,4′-benzoyl chloride, 2-chloroterephthaloylchloride, 2,5-dichloroterephthaloyl chloride, 2-methylterephthaloylchloride, 2,6-naphthalenedicarboxylic acid chloride, and1,5-naphthalenedicarboxylic acid chloride. Suitable aromatic diaminesinclude para-phenylenediamine, 4,4′-diaminobiphenyl,2-methyl-paraphenylenediamine, 2-chloro-paraphenylenediamine,2,6-naphthalenediamine, 1,5-naphthalenediamine, and4,4′-diaminobenzanilide.

In some embodiments, the present invention is related to a process thatproduces fiber derived from the polymerization of5(6)-amino-2-(p-aminophenyl)benzimidazole, para-phenylenediamine, andterephthaloyl dichloride at high solids (7 weight percent or greater) inNMP/CaCl₂ or DMAC/CaCl₂, isolates the copolymer crumb, dissolves theisolated copolymer crumb in concentrated sulfuric acid to form a liquidcrystalline solution, and spins the solution into fibers.

The copolymerization reaction of5(6)-amino-2-(p-aminophenyl)benzimidazole, para-phenylenediamine, andterephthaloyl dichloride can be accomplished by means known in the art.See, for example, PCT Patent Application No. 2005/054337 and U.S. PatentApplication No. 2010/0029159. Typically, one or more acid chloride(s)and one or more aromatic diamine(s) are reacted in an amide polarsolvent such as N,N-dimethylformamide, N,N-dimethylacetamide,N-methyl-2-pyrrolidone, dimethylimidazolidinone and the like.N-methyl-2-pyrrolidone is preferred in some embodiments.

In some embodiments, before or during the polymerization, a solubilityagent of an inorganic salt such as lithium chloride, or calciumchloride, or the like is added in a suitable amount to enhance thesolubility of the resulting copolyamide in the amide polar solvent.Typically, 3 to 10% by weight relative to the amide polar solvent isadded. After the desired degree of polymerization has been attained, thecopolymer is present in the form of an un-neutralized crumb. By “crumb”it is meant the copolymer is in the form of a friable material or gelthat easily separates into identifiable separate masses when sheared.The un-neutralized crumb includes the copolymer, the polymerizationsolvent, the solubility agent and the byproduct acid from thecondensation reaction, typically hydrochloric acid (HCl).

After completing the polymerization reaction, the un-neutralized crumbcan optionally be contacted with a base, which can be a basic inorganiccompound, such as sodium hydroxide, potassium hydroxide, calciumhydroxide, calcium oxide, ammonium hydroxide, and the like. The basicinorganic compound can be used in aqueous solution to perform aneutralization reaction of HCl by-product. If desired, the basiccompound can be an organic base such as diethyl amine or tributyl amineor other amines. Typically, the un-neutralized copolymer crumb iscontacted with the aqueous base by washing, which converts acidicbyproduct to a salt (generally a sodium chloride salt if sodiumhydroxide is the base and HCl is the acidic byproduct) and also removessome of the polymerization solvent. If desired, the un-neutralizedcopolymer crumb can be optionally first washed one or more times withwater prior to contacting with the basic inorganic compound to removeexcess polymerization solvent. Once the acidic byproduct in thecopolymer crumb is neutralized, additional water washes can be employedto remove salt and polymerization solvent and lower the pH of the crumb,if needed.

The copolymer typically has an inherent viscosity of at least 3 dl/g,preferably at least 5 dl/g or higher. In some embodiments, the inherentviscosity can be 6 dl/g or greater.

The copolymer is preferably spun into fiber using solution spinning.Generally this involves solutioning the copolymer crumb in a suitablesolvent to form a spin solution (also known as spin dope), the preferredsolvent being sulfuric acid. The inventors have found that the use ofcopolymer crumb that has been neutralized as described hereindramatically reduces the formation of bubbles in the spin dope when suchneutralized crumb is combined with sulfuric acid in the solutioningprocess. If the copolymer crumb is not neutralized, hydrochloric acidby-product in the copolymer can volatize on contact with the sulfuricacid and form bubbles in the spin dope. Since the solution viscosity ofthe spin dope is relatively high, bubbles that are formed duringsolutioning tend to stay in the spin dope and are spun into thefilaments unless further steps are provided for their removal. Theneutralized copolymer crumb, when solutioned in sulfuric acid, providesan essentially bubble-free and therefore more uniform spinning solutionwhich is believed to provide more uniformly superior copolymer filamentsand fibers.

The spin dope containing the copolymer described herein can be spun intodope filaments using any number of processes; however, wet spinning and“air-gap” spinning are the best known. The general arrangement of thespinnerets and baths for these spinning processes is well known in theart, with the figures in U.S. Pat. Nos. 3,227,793; 3,414,645; 3,767,756;and 5,667,743 being illustrative of such spinning processes for highstrength polymers. In “air-gap” spinning the spinneret typicallyextrudes the fiber first into a gas, such as air and is a preferredmethod for forming filaments

It is believed that in addition to producing the spinning dope withneutralized copolymer crumb, for the best fiber properties, themanufacturing process of spinning fibers from an acid solvent shouldadditionally include steps that extract acid solvent from the filaments.It is believed that failure to do this can result in more potentialdegradation of the copolymer in the fiber and subsequent decrease infiber mechanical properties over time.

What the inventors have found is that traditional methods ofneutralizing acid-containing as-spun fibers impacts the final tenacitythat can be achieved by that fiber. Generally, prior art methods havebeen to neutralize the fiber with a simple strong base, most typicallyNaOH.

One process for making copolymer filaments or yarns is shown in FIG. 1.The dope solution 2, comprising copolymer and sulfuric acid, typicallycontains a high enough concentration of polymer for the polymer to forman acceptable filament 6 after extrusion and 12 after coagulation. Whenthe polymer is lyotropic liquid-crystalline, the concentration ofpolymer in the dope 2 is preferably high enough to provide aliquid-crystalline dope. The concentration of the polymer is preferablyat least about 12 weight percent, more preferably at least about 16weight percent and most preferably at least about 20 weight percent. Theconcentration of the polymer is preferably less than about 30 weightpercent, more preferably less than about 28 weight percent.

The polymer dope solution 2 may contain additives such as anti-oxidants,lubricants, ultra-violet screening agents, colorants and the like whichare commonly incorporated. The spin dope solvent may containco-solvents, but is principally sulfuric acid. In some embodiments thesulfuric acid is concentrated sulfuric acid and in some preferredembodiments, the sulfuric acid has a concentration of 99 to 101 percent.In some embodiments, the sulfuric acid has a concentration of greaterthan 100 percent.

The polymer dope solution 2 is typically extruded or spun through a dieor spinneret 4 to prepare or form the dope filaments 6. The spinneret 4preferably contains a plurality of holes. The number of holes in thespinneret and their arrangement is not critical, but it is desirable tomaximize the number of holes for economic reasons. The spinneret 4 cancontain as many as 100 or 1000, or more, and they may be arranged incircles, grids, or in any other desired arrangement. The spinneret 4 maybe constructed out of any materials that will not be severely degradedby the dope solution 2.

The spinning process of FIG. 1 employs “air-gap” spinning (alsosometimes known as “dry-jet” wet spinning). Dope solution 2 exits thespinneret 4 and enters a gap 8 (typically called an “air gap” althoughit need not contain air) between the spinneret 4 and a coagulation bath10 for a very short duration of time. The gap 8 may contain any fluidthat does not induce coagulation or react adversely with the dope, suchas air, nitrogen, argon, helium, or carbon dioxide. The dope filament 6proceeds across the air gap 8, and is immediately introduced into aliquid coagulation bath. Alternately, the fiber may be “wet-spun” (notshown). In wet spinning, the spinneret typically extrudes the fiberdirectly into the liquid of a coagulation bath and normally thespinneret is immersed or positioned beneath the surface of thecoagulation bath. Either spinning process may be used to provide fibersfor use in the processes of the invention. In some embodiments of thepresent invention, air-gap spinning is preferred.

The filament 6 is “coagulated” in the coagulation bath 10. In someembodiments the coagulation bath contains water or a mixture of waterand sulfuric acid. If multiple filaments are extruded simultaneously,they may be combined into a multifilament yarn before, during or afterthe coagulation step. The term “coagulation” as used herein does notnecessarily imply that the dope filament 6 is a flowing liquid andchanges into a solid phase. The dope filament 6 can be at a temperaturelow enough so that it is essentially non-flowing before entering thecoagulation bath 10. However, the coagulation bath 10 does ensure orcomplete the coagulation of the filament, i.e., the conversion of thepolymer from a dope solution 2 to a substantially solid polymer filament12. The amount of solvent, i.e., sulfuric acid, removed during thecoagulation step will depend on variables such as the residence time ofthe filament 6 in the coagulation bath, the temperature of the bath 10,and the concentration of solvent therein.

After the coagulation bath, the fiber 12 may be contacted with one ormore washing baths or cabinets 14. Washes may be accomplished byimmersing the fiber into a bath, by spraying the fiber with the aqueoussolution, or by other suitable means. Washing cabinets typicallycomprise an enclosed cabinet containing one or more rolls which the yarntravels across a number of times prior to exiting the cabinet.

The temperature of the washing fluid(s) is adjusted to provide a balanceof washing efficiency and practicality and is greater than about 0° C.and preferably less than about 70° C. The washing fluid may also beapplied in vapor form (steam), but is more conveniently used in liquidform. Preferably, a number of washing baths or cabinets are used. In acontinuous process, the duration of the entire washing process in thepreferred multiple washing bath(s) and/or cabinet(s) is preferably nogreater than about 10 minutes. In some embodiments the duration of theentire washing process is 5 seconds or more; in some embodiments theentire washing is accomplished in 400 seconds or less. In a batchprocess, the duration of the entire washing process may be on the orderof hours, as much as 12 to 24 hours or more.

The inventors have found that a majority of the sulfuric acid solvent israpidly washed from the fiber while a portion of the solvent is removedmuch more slowly. While not being bound by any specific theory it isbelieved that as a result of the acidic environment, a portion of thesulfuric acid may exist as sulfate anions associated with protonatedimidazole moieties, and is more slowly removed during water washing. Theinventors have found that certain wash solutions remove sulfuric acidfaster than solely water washing. Additionally, the inventors have foundthat certain washing fluids are detrimental to the development oftensile properties. Specifically washing with strong bases (those thatfully dissociate in aqueous solution) such as NaOH as practiced in theart is advantageous to the rapid removal of residual acid solvent,however the inventors have found that application of strong bases suchas NaOH for final washing or neutralization prior to any final rinsingas practiced in the art is detrimental to the development of tensileproperties.

In some embodiments, the as-spun multi-filament yarn is washed with anaqueous acid comprising a halide or an aqueous salt comprising a halideor combination thereof. In some embodiments, the acid comprising ahalide is one or more of hydrofluoric acid, hydrochloric acid,hydrobromic acid, hydroiodic acid, or mixtures thereof. In certainembodiments, salt comprising a halide is sodium chloride, sodiumbromide, potassium chloride, potassium bromide, lithium chloride,lithium bromide, calcium chloride, calcium bromide, magnesium chloride,magnesium bromide, ammonium chloride, ammonium bromide, ferrouschloride, ferrous bromide, ferric chloride, ferric bromide, zincchloride, zinc bromide, or mixtures of two or more of these.

In some embodiments, the fiber may be additionally washed or rinsed withwater. Following these steps, it is believed halide anions are nowassociated with protonated imidazoles; that, is they are ionically boundto the polymer.

The fiber or yarn 12, after washing, may be dried in a dryer 20 toremove water and other fluids. One or more dryers may be used. Incertain embodiments, the dryer may be an oven which uses heated air todry the fibers. In other embodiments, heated rolls may be used to heatthe fibers. The fiber is heated in the dryer to a temperature of atleast about 20° C. but less than about 200° C., more preferably lessthan about 100° C. until the moisture content of the fiber is 20 weightpercent of the fiber or less. In some embodiments the fiber is heated to85° C. or less. In some embodiments the fiber is heated under thoseconditions until the moisture content of the fiber is 14 weight percentof the fiber or less. The inventors have discovered that low temperaturedrying is a preferred route to improved fiber strength. Specifically,the inventors have found that the best fiber strength properties areachieved when the first drying step (i.e. heated roll, heated atmosphereas in an oven, etc.) experienced by the never-dried yarn is conducted atgentle temperatures not normally used in continuous processes used todry high strength fibers on commercial scale. It is believed that thecopolymer fiber has more affinity to water than PPD-T homopolymer; thisaffinity slows the diffusion rate of water out of the polymer duringdrying and consequently if the never-dried yarn is directly exposed totypical high drying temperatures, generally used to create a largethermal driving force and reduce drying time, irreparable damage to thefiber occurs resulting in lower fiber strength. In some embodiments, thefiber is heated at least to about 30° C.; in some embodiments the fiberis heated at least to about 40° C.

The dryer residence time is less than ten minutes and is preferably lessthan 180 seconds. The dryer can be provided with a nitrogen or othernon-reactive atmosphere. The drying step typically is performed atatmospheric pressure. If desired, however, the step may be performedunder reduced pressure. In one embodiment, the filaments are dried undera tension of at least 0.1 gpd, preferably a tension of 2 gpd or greater.

Following the drying step, the fiber is preferably further heated to atemperature of at least 350° C. in, for instance, a heat setting device22. One or more devices may be utilized. For example, such processingmay be done in a nitrogen purged tube furnace 22 for increasing tenacityand/or relieving the mechanical strain of the molecules in thefilaments. In some embodiments, the fiber or yarn is heated to atemperature of at least 400° C. In one embodiment, the filaments areheated under a tension of 1 gpd or less.

In some embodiments, the heating is a multistep process. For example, ina first step the fiber or yarn may be heated at a temperature of 200 to360° C. at a tension of at least 0.2 cN/dtex, followed by a secondheating step where the fiber or yarn is heated at a temperature of 370to 500° C. at a tension of less than 1 cN/dtex.

Finally, the yarn 12 is wound up into a package on a windup device 24.Rolls, pins, guides, and/or motorized devices 26 are suitably positionedto transport the filament or yarn through the process. Such devices arewell known in the art and any suitable device may be utilized.

Molecular weights of polymers are typically monitored by, and correlatedto, one or more dilute solution viscosity measurements. Accordingly,dilute solution measurements of the relative viscosity (“V_(rel)” or“η_(rel)” or “n_(rel)”) and inherent viscosity (“V_(inh)” or “η_(inh)”or “n_(inh)”) are typically used for monitoring polymer molecularweight. The relative and inherent viscosities of dilute polymersolutions are related according to the expressionV _(inh)=ln(V _(rel))C,where ln is the natural logarithm function and C is the concentration ofthe polymer solution. V_(rel) is a unitless ratio, thus V_(inh) isexpressed in units of inverse concentration, typically as deciliters pergram (“dl/g”).

The invention is further directed, in part, to fabrics that includefilaments or yarns of the present invention, and articles that includefabrics of the present invention. For purposes herein, “fabric” meansany woven, knitted, or non-woven structure. By “woven” is meant anyfabric weave, such as, plain weave, crowfoot weave, basket weave, satinweave, twill weave, and the like. By “knitted” is meant a structureproduced by interlooping or intermeshing one or more ends, fibers ormultifilament yarns. By “non-woven” is meant a network of fibers,including unidirectional fibers (optionally contained within a matrixresin), felt, and the like.

Definitions

As used herein, the term “residue” of a chemical species refers to themoiety that is the resulting product of the chemical species in aparticular reaction scheme or subsequent formulation or chemicalproduct, regardless of whether the moiety is actually obtained from thechemical species. Thus, a copolymer comprising residues of paraphenylenediamine refers to a copolymer having one or more units of the formula:

Similarly, a copolymer comprising residues of DAPBI contains one or moreunits of the structure:

A copolymer having residues of terephthaloyl dichloride contains one ormore units of the formula:

The term “polymer,” as used herein, means a polymeric compound preparedby polymerizing monomers, end-functionalized oligomers, and/orend-functionalized polymers whether of the same or different types. Theterm “copolymer” (which refers to polymers prepared from at least twodifferent monomers), the term “terpolymer” (which refers to polymersprepared from three different types of monomers), and the term“quadpolymer (which refers to polymers having four different types ofmonomers) are included in the definition of polymer. In someembodiments, all monomers can be reacted at once to form the polymer. Insome embodiments, monomers can be reacted sequentially to form oligomerswhich can be further reacted with one or more monomers to form polymers.

By “oligomer,” it is meant polymers or species eluting out at <3000 MWwith a column calibrated using polyparaphenylene diamine terephthalamidehomopolymer.

As used herein, “stoichiometric amount” means the amount of a componenttheoretically needed to react with all of the reactive groups of asecond component. For example, “stoichiometric amount” refers to themoles of terephthaloyl dichloride needed to react with substantially allof the amine groups of the amine component (paraphenylene diamine andDAPBI). It is understood by those skilled in the art that the term“stoichiometric amount” refers to a range of amounts that are typicallywithin 10% of the theoretical amount. For example, the stoichiometricamount of terephthaloyl dichloride used in a polymerization reaction canbe 90-110% of the amount of terephthaloyl dichloride theoreticallyneeded to react with all of the paraphenylene diamine and DAPBI aminegroups.

“Fiber” means a relatively flexible, unit of matter having a high ratioof length to width across its cross-sectional area perpendicular to itslength. Herein, the term “fiber” is used interchangeably with the term“filament”. The cross section of the filaments described herein can beany shape, but are typically circular or bean shaped. Fiber spun onto abobbin in a package is referred to as continuous fiber. Fiber can be cutinto short lengths called staple fiber. Fiber can be cut into evensmaller lengths called floc. The fibers of the invention are generallysolid with minimal voids. The term “yarn” as used herein includesbundles of filaments, also known as multifilament yarns; or towscomprising a plurality of fibers; or spun staple yarns. Yarn mayoptionally be intertwined and/or twisted.

The term “organic solvent” is understood herein to include a singlecomponent organic solvent or a mixture of two or more organic solvents.In some embodiments, the organic solvent is dimethylformamide,dimethylacetamide (DMAC), N-methyl-2-pyrrolidone (NMP), ordimethylsulfoxide. In some preferred embodiments, the organic solvent isN-methyl-2-pyrrolidone or dimethylacetamide.

The term “inorganic salt” refers to a single inorganic salt or to amixture of two or more inorganic salts. In some embodiments, theinorganic salt is sufficiently soluble in the solvent and liberates anion of a halogen atom. In some embodiments, the preferred inorganic saltis KCl, ZnCl₂, LiCl or CaCl₂. In certain preferred embodiments, theinorganic salt is LiCl or CaCl₂.

By “never-dried” it is meant the moisture content of the fiber made fromthese polymers has never been lower than at least about 25 weightpercent of the fiber.

By “solids” it is meant the ratio of the mass of copolymer (neutralbasis) to the total mass of the solution, this is, the mass of copolymerplus solvent.

As used in the specification including the appended claims, the singularforms “a,” “an,” and “the” include the plural, and reference to aparticular numerical value includes at least that particular value,unless the context clearly dictates otherwise. When a range of values isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Allranges are inclusive and combinable. When any variable occurs more thanone time in any constituent or in any formula, its definition in eachoccurrence is independent of its definition at every other occurrence.Combinations of substituents and/or variables are permissible only ifsuch combinations result in stable compounds.

Test Methods

Yarn tenacity is determined according to ASTM D 885 and is the maximumor breaking stress of a fiber as expressed as either force per unitcross-sectional area, as in giga-Pascals (GPa), or in force per unitmass per length, as in grams per denier or grams per dtex.

Inherent viscosity is determined using a solution in which a polymer isdissolved in concentrated sulfuric acid with a concentration of 96 wt %at a polymer concentration (C) of 0.5 g/dl and at a temperature of 25°C. Inherent viscosity is then calculated as ln (t_(poly)/t_(solv))/Cwhere t_(poly) is the drop time for the polymer solution and t_(solv) isthe drop time of the pure solvent.

Percent sulfur determined by combustion is measured according to ASTMD4239 Method B. A carefully weighed amount of sample (typically 2.5-4.5mg) and of vanadium pentoxide accelerant (typically 10 mg) is placed ina tin capsule. The capsule is then dropped into an oxidation/reductionreactor kept at a temperature of 900-1000° C. The exact amount of oxygenrequired for optimum combustion of the sample is delivered into thecombustion reactor at a precise time. The exothermic reaction withoxygen raises the temperature to 1800° C. for a few seconds. At thishigh temperature both organic and inorganic substances are convertedinto elemental gases which, after further reduction (to nitrogen, carbondioxide, water and sulfur dioxide), are separated in a chromatographiccolumn and finally detected by a highly sensitive thermal conductivitydetector (TCD).

Typical Running Conditions for Carbon, Hydrogen, Nitrogen, and Sulfur(CHNS):

Method setpoints CHNS Left Furnace (° C.) 950 Oven (° C.) 75 Carrier(ml/min) 140 Oxygen (ml/min) 250 Reference (ml/min) 150 Cycle (Run Time)(sec) 480 Sampling Delay (sec) 12 Oxygen Injection End 5 (sec)

Four samples of BBOT ((5-tert-butyl-benzoxazol-2yl) thiophene. C=72.53%H=6.09% N=6.51% S=7.44%) standard for sulfur are run to develop thecalibration curve. Once the calibration curve is verified, samples areanalyzed.

The operation of a High Temperature Tube Furnace is described in ASTMD4239-10: “Sulfur in the Analysis Sample of Coal and Coke Using HighTemperature Tube Furnace Combustion.”

For better precision of sulfur content below 0.05 weight percent, it isdesirable to use the following technique. A clean 100-mL Quartz crucibleis placed on a 4 decimal place analytical balance and the balance iszeroed. Between 0.3 g-0.6 g of fiber or polymer resin is weighed intothe crucible. Small amounts of 0.1 N sodium hydroxide are carefullyadded to the fiber or polymer resin sample until it is barely coveredwith the solution. The sample is allowed to set in the solution for 15minutes. The fiber or polymer resin is heated on a hotplate at atemperature of 190 deg C. The solution is allowed to slowly evaporate.This step usually takes about 30 minutes. After the solution hascompletely evaporated in the 100-mL crucible, the crucible is placed ina muffle furnace set at a temperature of 600 deg C. The sample isallowed to ash for 5 hours. After the 5 hour ashing time, the crucibleis removed from the muffle furnace and allowed to cool for 30 minutes. 2mL of concentrated environmental grade nitric acid is added to the 25-mLgraduated cylinder and the cylinder is then filled to the 25 mL markwith Milli-Q Water. The acid solution is transferred from the 25-mLgraduated cylinder to the 100-mL crucible containing the ashed material.As soon as the acid solution is added, the ash immediately dissolves.The acid solution is transferred from the 100-mL crucible to a 15-mLplastic centrifuge tube. The acid solution is then analyzed in the axialmode by a Perkin Elmer 5400 DV ICP Emission Spectrometer using the181.975 nm Sulfur Emission line. The ICP Emission Spectrometer iscalibrated using a blank, a 10 ppm Sulfur Standard, and a 100 ppm Sulfurstandard. The ICP standards were prepared by High Purity Standardslocated in Charleston, S.C.

Percent halogen in the fiber can be determined via XRF, or CIC, or othersuitable methods known to those skilled in the art. To distinguishbetween ionic forms of halogens remaining in the fiber from halogensubstituents on monomer residues further techniques are useful. Forexample, TGA-IR (ASTM E2105-00) may be used to distinguish ionichalogens released at lower temperatures from halogen substituents onmonomer residues that are released during degradation at highertemperatures. For example, FIGS. 2, 3, and 4 illustrate the use ofTGA-IR as a means of differentiating chloride anions from covalentlybonded chlorine. FIG. 2 compares HCl evolution profiles (Chemigrams)identified via monitoring of the appropriate IR spectral region duringheating of a sample (A) containing ionic chlorides versus a sample (B)containing a chlorine ring substituent. FIGS. 3 and 4 illustrate thecorresponding weight loss provided by TGA.

Moisture content of the fiber was obtained by first weighing the fibersample, placing the sample in an oven at 300° C. for 20 minutes, thenimmediately re-weighing the sample. Moisture content is then calculatedby subtracting the dried sample weight from the initial sample weightand dividing by the dried sample weight times 100%.

Many of the following examples are given to illustrate variousembodiments of the invention and should not be interpreted as limitingit in any way. All parts and percentages are by weight unless otherwiseindicated.

EXAMPLES Polymer Example 1

N-methyl-2-pyrrolidone (NMP) solvent containing calcium chloride (CaCl₂)in amounts appropriate for the final solution concentration was chargedin a FM130D Littleford Reactor. Appropriate amounts of the monomer5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI) and terephthaloyldichloride (TCL) were then added to the reactor and reacted to formoligomers. To this mixture, appropriate amounts of para-phenylenediamine(PPD) and TCL were added to form a finished copolymer crumb. The crumbwas ground into smaller particles and then first washed with a sodiumhydroxide solution to neutralize reaction byproducts and then with waterto remove NMP. The polymer was then recovered, dried, and its inherentviscosity determined as summarized in Table 1.

TABLE 1 Inherent DAPBI/PPD Viscosity Item molar ratio (dl/g) P1-1 50/506.10 P1-2 60/40 6.13 P1-3 70/30 5.90

Polymer Example 2

N-methyl-2-pyrrolidone (NMP) solvent containing calcium chloride (CaCl₂)in amounts appropriate for the final solution concentration was chargedin a FM130D Littleford Reactor. Appropriate amounts of the monomer5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI), PPD and a portion ofterephthaloyl dichloride (TCL) were then added to the reactor andreacted to form oligomers. To this mixture, appropriate amounts of TCLwere added to form a finished copolymer crumb. The crumb was ground intosmaller particles and then first washed with a sodium hydroxide solutionto neutralize reaction byproducts and then with water to remove NMP. Thepolymer was then recovered, dried, and its inherent viscosity determinedas summarized in Table 2.

TABLE 2 Inherent DAPBI/PPD Viscosity Item molar ratio (dl/g) P2-1 40/607.00 P2-2 50/50 6.39 P2-3 75/25 3.98

Fiber Examples

In the following examples, solution spinning of copolymers inconcentrated sulfuric acid was employed to form yarns using dry jet wetspinning processes similar to that used for para-aramid homopolymers.See, U.S. Pat. No. 3,767,756.

Comparative Example A

A polymer solution in concentrated sulfuric acid having a concentrationof 25 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio. The copolymer solution wasspun through a spinneret having 270 holes, to produce nominal lineardensity of 3.0 denier per filament. Yarn was coagulated and water washedto 2.98 weight percent sulfur.

The yarn was then continuously washed in 9 wash cabinets at 100 m/min.The sixth cabinet employed NaOH wash solutions as given in Table 3 withall other cabinets employing water. The first wash cabinet employed 10advancing wraps through wash sprays and applicators while the remaining8 wash cabinets employed 20 advancing wraps through wash sprays andapplicators. All wash modules were operated at 60° C. The yarn was driedin-line at 0.5 g/denier tension with a temperature ramp from 130° C. to205° C. along the length of the oven. The yarn was then heat treated at0.5 g/denier tension using a maximum temperature of 408° C. The residualsulfur measured by combustion, residual sodium, and final tenacity ofthe heat treated yarns is shown in Table 3.

TABLE 3 NaOH Concentration Residual Residual HT Cabinet 6 S Na TenacityItem (wt %) (wt % S) (wt % Na) (gpd) C-A1 0.5 2.22 0.26 28.4 C-A2 1.02.17 0.35 27.3 C-A3 1.5 2.07 0.48 27.2 C-A4 2.0 2.04 0.59 27.1 C-A5 2.51.99 0.61 24.6 C-A6 3.0 1.96 0.69 25.4

Example 1 and Comparative Example B

A polymer solution in concentrated sulfuric acid having a concentrationof 22 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio. The copolymer solution wasspun through a spinneret having 270 holes, to produce nominal lineardensity of 1.75 denier per filament. Yarn was coagulated and waterwashed to 3.00 weight percent sulfur.

The yarn was continuously washed in 9 wash cabinets at 24 m/min. Thesecond cabinet employed HCl wash solutions as given in Table 4 with allother cabinets employing water. The first wash cabinet employed 10advancing wraps through wash sprays and applicators while the remaining8 wash cabinets employed 20 advancing wraps through wash sprays andapplicators. All wash modules were operated at 60° C. The yarn was driedin-line at 0.5 g/denier tension with a temperature ramp from 130° C. to205° C. along the length of the oven. The yarn was then heat treated at0.5 g/denier tension using a maximum temperature of 415° C. The residualsulfur measured by combustion and final tenacity of the heat treatedyarns are shown in Table 4.

TABLE 4 HCl Residual HT Concentration S Tenacity Item (wt %) (wt % S)(gpd) C-B1 0 1.87 24.8 1-1 0.25 1.24 26.0 1-2 0.5 0.78 29.1 1-3 1 0.5830.0 1-4 2 0.46 31.3

Example 2

A polymer solution in concentrated sulfuric acid having a concentrationof 24 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio having an inherent viscosityof 5.9. The copolymer solution was spun through a spinneret having 270holes, to produce a nominal linear density of 1.5 denier per filament.Yarn was coagulated and water washed as in example 1.

The yarn was then continuously washed in 9 wash cabinets at 100 m/min.The fourth cabinet employed 5 wt % aqueous HCl wash solution with allother cabinets employing water. All wash cabinets employed 10 advancingwraps through wash sprays and applicators and were maintained at 60° C.The yarn was dried in-line on 70° C. heated rolls at 0.5 g/deniertension.

The yarn was then heat treated at 0.5 g/denier tension using a maximumtemperature of 400° C. Tensile properties after heat treatment were:tenacity 36.2 g/denier, elongation 3.94% and initial modulus 887g/denier. This sample had a residual sulfur content measured bycombustion of 1.01 wt %.

Example 3

A polymer solution in concentrated sulfuric acid having a concentrationof 22 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio. The copolymer solution wasspun through a spinneret having 270 holes, to produce nominal lineardensity of 1.5 denier per filament. Yarn was coagulated and water washedto 2.97 weight percent sulfur.

The yarn was continuously washed in 9 wash cabinets with different linespeeds corresponding to residence times and number of advancing wraps.The fourth cabinet employed HCl wash solutions as given in Table 5 withall other cabinets employing water. The first wash cabinet employed 10advancing wraps through wash sprays and applicators while the remaining8 wash cabinets employed all the same number of advancing wraps either10 or 20 through wash sprays and applicators. All wash modules wereoperated at 60° C. The yarn was dried in-line at 0.5 g/denier tension onheated rolls at a temperature of 70° C.

The yarn was then heat treated at 0.5 g/denier tension using a maximumtemperature of 415° C. The residual sulfur measured by combustion,residual chlorine before heat treatment, and final tenacity of the heattreated yarns are given in Table 5.

TABLE 5 HCl Concen- Time in Residual Residual HT tration Wash solution SCl Tenacity Item (wt %) Stages (sec) (wt % S) (wt % Cl) (gpd) 3-1 2 107.5 1.40 3.56 30.9 3-2 2 20 15 0.89 3.38 31.7 3-3 2 10 15 1.00 3.41 32.43-4 2 20 30 0.61 3.36 32.8 3-5 2 10 60 0.41 3.88 32.2 3-6 2 20 120 0.283.37 31.3 3-7 5 20 30 0.69 3.60 31.0 3-8 5 20 30 0.65 3.87 31.1 3-9 5 2030 0.60 4.47 31.2 3-10 5 20 30 0.55 5.26 31.0

Comparative Example C and Example 4

A polymer solution in concentrated sulfuric acid having a concentrationof 25 wt % solids was formed using a 5.9 dL/g inherent viscosityneutralized copolymer made from TCl and a 70/30 DAPBI/PPD diamine molarratio. The dope was mixed for 3 hours at 85° C. and extruded at 73° C.through a 9-hole spinneret with 76.2 micron capillary diameters.Filaments were drawn through a 3 mm air gap and coagulated in a quenchbath at approximately 2° C. at speeds appropriate for producing a rangeof linear densities. Fiber samples were washed by one of three methods:Wash1—in an overflowing water bath for 24 hours; Wash2—in an overflowingwater bath for 24 hours followed by a neutralization in 0.1 wt % aqueousNaOH for 10 minutes; or Wash3—a 30 minute exposure to 0.25 wt % aqueousNaCl. Samples were then heat treated with a maximum temperature of 390°C. under a tension of 0.4 gpd. The as-spun yarn sulfur content wasdetermined by combustion and chlorine content was determined by IonChromatography (IC). Sulfur values are listed in Table 6 along with theheat treated yarn tensile properties determined according to ASTM D 885,using yarn plied 8 times to improve the accuracy of the measurements.Reported plied denier values represent 8 times the denier value of thespun yarn. Items treated with Wash3 were found to contain 0.2 to 1.8 wt% chloride prior to heat treatment.

TABLE 6 Wash Plied Tenacity Elongation Modulus S Item Type Denier (gpd)(%) (gpd) (wt %) C-C1 Wash1 168 31.6 3.10 981 0.71 C-C2 Wash1 115 32.83.18 989 0.54 C-C3 Wash2 180 23.6 2.50 998 0.42 C-C4 Wash2 117 25.0 2.531000 0.50 4-1 Wash3 193 34.6 3.56 954 2.27 4-2 Wash3 136 35.0 3.51 9782.03

Example 5

Polymer solutions in concentrated sulfuric acid were formed usingneutralized copolymers made from TCl and a 70/30 DAPBI/PPD diamine molarratio. Each copolymer solution was spun through a spinneret having 270holes and different conditions employed to produce a range of filamentdeniers.

Never-dried samples for further washing were prepared by non-overlappedwinding of approximately 100 m lengths onto perforated plastic cores.Wash experiments were performed at room temperature in a sequence ofthree separate but consecutive soaking baths. Bath 1 employed fresh 2 wt% HCl wash solutions and baths 2, and 3 were fresh water washing bathsfor each. Washing time was 30 minutes in each of the consecutive baths.

After washing, samples were air dried overnight. Samples were then heattreated to 415° C. under a tension of 0.5 g/denier. Residual sulfurmeasured by combustion, chlorine before heat treatment, chlorine afterheat treatment, and heat treated tenacities are summarized in Table 7.

TABLE 7 Nominal Pre HT Post HT denier Residual Residual HT Residual perS Cl Tenacity Cl Item filament (wt % S) (wt % Cl) (gpd) (wt % Cl) 5-11.5 0.07 3.51 25.1 0.38 5-2 2.0 0.20 3.90 29.6 0.30 5-3 1.5 0.07 3.6829.3 0.41 5-4 2.25 0.11 3.80 27.7 0.44 5-5 1.75 0.08 2.83 29.9 0.50

Example 6 and Comparative Example D

A polymer solution in concentrated sulfuric acid having a concentrationof 22 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio having an inherent viscosityof 5.33. The copolymer solution was spun through a spinneret having 270holes, to produce a nominal linear density of 1.75 denier per filament.Yarn was coagulated and water washed to a sulfur level of 3.0 wt %.

Never-dried samples for further washing were prepared by non-overlappedwinding of approximately 100 m lengths onto perforated plastic cores.Wash experiments were performed at room temperature in a sequence ofthree separate but consecutive soaking baths. Bath 1 employed the washsolutions indicated in Table 8. Baths 2 and 3 were fresh water washingbaths for each sample. Washing time was 30 minutes in each of theconsecutive baths.

After washing, samples were air dried overnight, then further dried inan oven at 50° C. for 4 hours. Samples were then heat treated to 415° C.under a tension of 0.5 g/denier. Residual sulfur measured by combustionand heat treated tenacities are summarized in Table 8. Yarn inherentviscosity was determined to be 3.7 dl/g.

TABLE 8 Bath 1 Residual HT Bath 1 Concentration S Tenacity Item Solute(wt %) (wt % S) (gpd) 6-1 NaCl 2 0.39 28.9 6-2 NaCl 5 0.63 29.3 6-3NH₄Cl 2 0.31 27.2 6-4 NH₄Cl 5 0.10 27.0 6-5 NaBr 2 0.48 29.3 6-6 CaCl₂ 20.53 28.9 6-7 CaCl₂ 5 1.20 27.1 6-8 HCl 2 0.15 29.0 6-9 HCl 5 0.05 28.5C-D1 Water 0 2.35 23.0

Example 7 and Comparative Example E

A polymer solution in concentrated sulfuric acid having a concentrationof 25 wt % solids was formed using a 6.69 dL/g inherent viscosityneutralized copolymer made from TCl and a 70/30 DAPBI/PPD diamine molarratio. The dope was mixed for 4 hours at 85° C. and extruded at 73° C.through a 9-hole spinneret with 76.2 micron capillary diameters.Filaments were drawn through a 3 mm air gap and coagulated in a quenchbath at approximately 2° C. at speeds appropriate for producing a rangeof linear densities. Fiber samples were washed by one of three methods:in an overflowing water bath for 48 hours, exposure to 0.25 wt % aqueousNaCl for 30 minutes, or exposure to 0.25 wt % aqueous LiCl for 30minutes. Samples were then heat treated with a maximum temperature of390° C. under a tension of 0.4 gpd. The dried as-spun yarn sulfurcontent was determined by combustion and chlorine content was determinedby Ion Chromatography (IC). Sulfur values are listed in Table 9 alongwith the heat treated yarn tensile properties determined according toASTM D 885, using yarn plied 8 times to improve the accuracy of themeasurements. Reported plied denier values represent 8 times the deniervalue of the spun yarn. Chloride levels of 1.8 to 2.8 wt % were found initems 7-1 to 7-4 prior to heat treatment.

TABLE 9 Wash Plied Tenacity Elongation Modulus S Item Type Denier (gpd)(%) (gpd) (wt %) C-E1 Water 224 33.6 3.47 987 <0.93 C-E2 Water 112 33.33.31 1033 <1.5 7-1 NaCl 238 35.6 3.69 958 1.93 7-2 NaCl 164 34.9 3.73951 2.56 7-3 LiCl 236 37.2 3.69 972 1.95 7-4 LiCl 160 34.2 3.56 960 2.25

Example 8 and Comparative Example F

A polymer solution in concentrated sulfuric acid having a concentrationof 25 wt % solids was formed using a 6.69 dL/g inherent viscosityneutralized copolymer made from TCl and a 70/30 DAPBI/PPD diamine molarratio. The dope was mixed for 3 hours at 85° C. and extruded at 73° C.through a 9-hole spinneret with 76.2 micron capillary diameters.Filaments were drawn through a 3 mm air gap and coagulated in a quenchbath at approximately 2° C. at speeds appropriate for producing a rangeof linear densities. Fiber samples were washed by one of three methods:a 48 hour wash in an overflowing water bath, a 30 minute water wash, ora 30 minute exposure to 0.25 wt % aqueous NaCl. Samples were then heattreated with a maximum temperature of 390° C. under a tension of 0.4gpd. The as-spun yarn sulfur was determined by combustion analysis andthe chlorine content was determined by Ion Chromatography (IC). Sulfurvalues are listed in Table 10 along with the heat treated yarn tensileproperties determined according to ASTM D 885, using yarn plied 8 timesto improve the accuracy of the measurements. Reported plied deniervalues represent 8 times the denier value of the spun yarn. Chloridelevels of 1.5 to 1.7 wt % were found in items 8-1 to 8-2 prior to heattreatment.

TABLE 10 Wash Plied Tenacity Elongation Modulus S Item Type Denier (gpd)(%) (gpd) (wt %) C-F1 48 hr 206 33.7 3.36 973 0.49 Water C-F2 48 hr 15333.7 3.39 965 0.56 Water C-F3 30 min 227 30.3 3.63 884 2.99 Water C-F430 min 166 30.6 3.62 884 3.19 Water 8-1 30 min 222 35.2 3.66 956 2.03NaCl 8-2 30 min 159 34.6 3.64 962 2.50 NaCl

Example 9

A polymer solution in concentrated sulfuric acid having a concentrationof 22 wt % solids was formed using a neutralized copolymer made from TCland a 70/30 DAPBI/PPD diamine molar ratio. The copolymer solution wasspun through a spinneret having 270 holes, to produce nominal lineardensity of 1.5 denier per filament. Yarn was coagulated and water washedto 2.97 weight percent sulfur.

The yarn was processed in 9 wash cabinets at 100 m/min. The fifthcabinet employed 5 wt % aqueous HCl wash solution with all othercabinets employing water. The first wash cabinet employed 10 advancingwraps while the remaining 8 wash cabinets employed all the same numberof advancing wraps either 10 or 20 as indicated in Table 11. All washmodule fluids were at 60° C. Wash sprays and applicators were active inthe first six wash cabinets. Optionally, sprays and applicators wereused to provide additional water washing in the remaining threecabinets. The yarn was dried in-line at 0.5 g/denier tension on heatedrolls at a temperature of 70° C.

Samples were then heat treated to 415° C. under a tension of 0.5g/denier. Residual sulfur measured by combustion, chlorine contentbefore heat treatment, and heat treated tenacities are summarized inTable 11

TABLE 11 Water washing Advancing Residual Pre HT HT modules wraps per SResidual Cl Tenacity Item after HCl module (wt % S) (wt % Cl) (gpd) 9-14 20 0.69 3.60 31.0 9-2 3 20 0.65 3.87 31.1 9-3 2 20 0.60 4.47 31.2 9-41 20 0.55 5.26 31.0 9-5 4 10 0.93 3.21 29.5 9-6 3 10 0.91 3.50 30.1 9-72 10 0.90 3.95 32.5 9-8 1 10 0.82 4.20 30.3

What is claimed:
 1. A fiber made from a polymer comprising imidazolegroups, the fiber further having: i) chlorine anions being present in anamount of 0.05 to 20.1 weight percent, based on weight of fiber; and ii)sulfur, wherein the sulfur is present in the fiber in an amount of 0.05to 3 weight percent, based on the weight of the fiber, the fiberexhibiting hydrochloric acid evolution as identified by TGA-IR between277.13° C. to 448.19° C.
 2. The fiber of claim 1, where the chlorineanions are present in an amount of 0.05 to 10 weight percent, based onweight of the fiber and sulfur is present in an amount of 0.05 to 1weight percent, based on the weight of the fiber.
 3. The fiber of claim1 wherein the chlorine anions are present in an amount of 0.1 to 5weight percent.
 4. The fiber of claim 3 wherein the chlorine anions arepresent in an amount of 0.1 to 1 weight percent.
 5. The fiber of claim1, wherein said polymer comprises residues of5(6)-amino-2-(p-aminophenyl) benzimidazole, aromatic diamine, andaromatic diacid-chloride.
 6. The fiber of claim 5, wherein said aromaticdiacid-chloride is terephthaloyl dichloride.
 7. The fiber of claim 5,wherein said aromatic diamine is para-phenylenediamine.
 8. The fiber ofclaim 5 having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of from 30/70 to 85/15.
 9. The fiberof claim 8, wherein the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 45/55 to 85/15.
 10. The fiber ofclaim 1 having 0.05 to 2.5 percent sulfur by weight, based on weight ofthe fiber.
 11. The fiber of claim 10 having 0.1 to 1.75 percent sulfurby weight, based on weight of the fiber.
 12. The fiber of claim 11having 0.1 to 1.0 percent sulfur by weight, based on weight of thefiber.
 13. A yarn comprising fiber of claim
 1. 14. The yarn of claim 13having a tenacity of 32 cN/dtex (35.6 gpd) or higher.
 15. The yarn ofclaim 14 having a tenacity of 34 cN/dtex (37.8 gpd) or higher.
 16. Theyarn of claim 15 having a tenacity of 36 cN/dtex (40 gpd) or higher. 17.Fabric comprising yarn of claim 13.